Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

3 files changed, 790 insertions, 0 deletions

diff --git a/src/nss-resolve/meson.build b/src/nss-resolve/meson.build
new file mode 100644
index 0000000..1fae426
--- /dev/null
+++ b/src/nss-resolve/meson.build
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+modules += [
+        nss_template + {
+                'name' : 'nss_resolve',
+                'conditions' : ['ENABLE_NSS_RESOLVE'],
+                'sources' : files('nss-resolve.c'),
+                'version-script' : meson.current_source_dir() / 'nss-resolve.sym',
+                'include_directories' : includes +
+                                        include_directories('../resolve'),
+        },
+]
diff --git a/src/nss-resolve/nss-resolve.c b/src/nss-resolve/nss-resolve.c
new file mode 100644
index 0000000..c4e02bc
--- /dev/null
+++ b/src/nss-resolve/nss-resolve.c
@@ -0,0 +1,759 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <netdb.h>
+#include <nss.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "env-util.h"
+#include "errno-util.h"
+#include "glyph-util.h"
+#include "in-addr-util.h"
+#include "macro.h"
+#include "nss-util.h"
+#include "resolved-def.h"
+#include "signal-util.h"
+#include "string-util.h"
+#include "strv.h"
+#include "varlink.h"
+
+static JsonDispatchFlags json_dispatch_flags = 0;
+
+static void setup_logging(void) {
+        log_parse_environment_variables();
+
+        if (DEBUG_LOGGING)
+                json_dispatch_flags = JSON_LOG;
+}
+
+static void setup_logging_once(void) {
+        static pthread_once_t once = PTHREAD_ONCE_INIT;
+        assert_se(pthread_once(&once, setup_logging) == 0);
+}
+
+#define NSS_ENTRYPOINT_BEGIN                    \
+        BLOCK_SIGNALS(NSS_SIGNALS_BLOCK);       \
+        setup_logging_once()
+
+NSS_GETHOSTBYNAME_PROTOTYPES(resolve);
+NSS_GETHOSTBYADDR_PROTOTYPES(resolve);
+
+static bool error_shall_fallback(const char *error_id) {
+        /* The Varlink errors where we shall signal "please fallback" back to the NSS stack, so that some
+         * fallback module can be loaded. (These are mostly all Varlink-internal errors, as apparently we
+         * then were unable to even do IPC with systemd-resolved.) */
+        return STR_IN_SET(error_id,
+                          VARLINK_ERROR_DISCONNECTED,
+                          VARLINK_ERROR_TIMEOUT,
+                          VARLINK_ERROR_PROTOCOL,
+                          VARLINK_ERROR_INTERFACE_NOT_FOUND,
+                          VARLINK_ERROR_METHOD_NOT_FOUND,
+                          VARLINK_ERROR_METHOD_NOT_IMPLEMENTED);
+}
+
+static bool error_shall_try_again(const char *error_id) {
+        /* The Varlink errors where we shall signal "can't answer now but might be able to later" back to the
+         * NSS stack. These are all errors that indicate lack of configuration or network problems. */
+        return STR_IN_SET(error_id,
+                          "io.systemd.Resolve.NoNameServers",
+                          "io.systemd.Resolve.QueryTimedOut",
+                          "io.systemd.Resolve.MaxAttemptsReached",
+                          "io.systemd.Resolve.NetworkDown");
+}
+
+static int connect_to_resolved(Varlink **ret) {
+        _cleanup_(varlink_unrefp) Varlink *link = NULL;
+        int r;
+
+        r = varlink_connect_address(&link, "/run/systemd/resolve/io.systemd.Resolve");
+        if (r < 0)
+                return r;
+
+        r = varlink_set_relative_timeout(link, SD_RESOLVED_QUERY_TIMEOUT_USEC);
+        if (r < 0)
+                return r;
+
+        *ret = TAKE_PTR(link);
+        return 0;
+}
+
+static uint32_t ifindex_to_scopeid(int family, const void *a, int ifindex) {
+        struct in6_addr in6;
+
+        if (family != AF_INET6 || ifindex == 0)
+                return 0;
+
+        /* Some apps can't deal with the scope ID attached to non-link-local addresses. Hence, let's suppress that. */
+
+        assert(sizeof(in6) == FAMILY_ADDRESS_SIZE(AF_INET6));
+        memcpy(&in6, a, sizeof(struct in6_addr));
+
+        return in6_addr_is_link_local(&in6) ? ifindex : 0;
+}
+
+static int json_dispatch_ifindex(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata) {
+        int *ifi = ASSERT_PTR(userdata);
+        int64_t t;
+
+        assert(variant);
+
+        if (!json_variant_is_integer(variant))
+                return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is not an integer.", strna(name));
+
+        t = json_variant_integer(variant);
+        if (t > INT_MAX)
+                return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is out of bounds for an interface index.", strna(name));
+
+        *ifi = (int) t;
+        return 0;
+}
+
+static int json_dispatch_family(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata) {
+        int *family = ASSERT_PTR(userdata);
+        int64_t t;
+
+        assert(variant);
+
+        if (!json_variant_is_integer(variant))
+                return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is not an integer.", strna(name));
+
+        t = json_variant_integer(variant);
+        if (t < 0 || t > INT_MAX)
+                return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is not a valid family.", strna(name));
+
+        *family = (int) t;
+        return 0;
+}
+
+typedef struct ResolveHostnameReply {
+        JsonVariant *addresses;
+        char *name;
+        uint64_t flags;
+} ResolveHostnameReply;
+
+static void resolve_hostname_reply_destroy(ResolveHostnameReply *p) {
+        assert(p);
+
+        json_variant_unref(p->addresses);
+        free(p->name);
+}
+
+static const JsonDispatch resolve_hostname_reply_dispatch_table[] = {
+        { "addresses", JSON_VARIANT_ARRAY,         json_dispatch_variant, offsetof(ResolveHostnameReply, addresses), JSON_MANDATORY },
+        { "name",      JSON_VARIANT_STRING,        json_dispatch_string,  offsetof(ResolveHostnameReply, name),      0              },
+        { "flags",     _JSON_VARIANT_TYPE_INVALID, json_dispatch_uint64,  offsetof(ResolveHostnameReply, flags),     0              },
+        {}
+};
+
+typedef struct AddressParameters {
+        int ifindex;
+        int family;
+        union in_addr_union address;
+        size_t address_size;
+} AddressParameters;
+
+static int json_dispatch_address(const char *name, JsonVariant *variant, JsonDispatchFlags flags, void *userdata) {
+        AddressParameters *p = ASSERT_PTR(userdata);
+        union in_addr_union buf = {};
+        JsonVariant *i;
+        size_t n, k = 0;
+
+        assert(variant);
+
+        if (!json_variant_is_array(variant))
+                return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is not an array.", strna(name));
+
+        n = json_variant_elements(variant);
+        if (!IN_SET(n, 4, 16))
+                return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is array of unexpected size.", strna(name));
+
+        JSON_VARIANT_ARRAY_FOREACH(i, variant) {
+                int64_t b;
+
+                if (!json_variant_is_integer(i))
+                        return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "Element %zu of JSON field '%s' is not an integer.", k, strna(name));
+
+                b = json_variant_integer(i);
+                if (b < 0 || b > 0xff)
+                        return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL),
+                                        "Element %zu of JSON field '%s' is out of range 0%s255.",
+                                        k, strna(name), special_glyph(SPECIAL_GLYPH_ELLIPSIS));
+
+                buf.bytes[k++] = (uint8_t) b;
+        }
+
+        p->address = buf;
+        p->address_size = k;
+
+        return 0;
+}
+
+static const JsonDispatch address_parameters_dispatch_table[] = {
+        { "ifindex", JSON_VARIANT_INTEGER,  json_dispatch_ifindex, offsetof(AddressParameters, ifindex), 0              },
+        { "family",  JSON_VARIANT_INTEGER,  json_dispatch_family,  offsetof(AddressParameters, family),  JSON_MANDATORY },
+        { "address", JSON_VARIANT_ARRAY,    json_dispatch_address, 0,                                    JSON_MANDATORY },
+        {}
+};
+
+static uint64_t query_flag(
+                const char *name,
+                const int value,
+                uint64_t flag) {
+        int r;
+
+        r = getenv_bool_secure(name);
+        if (r >= 0)
+                return r == value ? flag : 0;
+        if (r != -ENXIO)
+                log_debug_errno(r, "Failed to parse $%s, ignoring.", name);
+        return 0;
+}
+
+static uint64_t query_flags(void) {
+        /* Allow callers to turn off validation, synthetization, caching, etc., when we resolve via
+         * nss-resolve. */
+        return  query_flag("SYSTEMD_NSS_RESOLVE_VALIDATE", 0, SD_RESOLVED_NO_VALIDATE) |
+                query_flag("SYSTEMD_NSS_RESOLVE_SYNTHESIZE", 0, SD_RESOLVED_NO_SYNTHESIZE) |
+                query_flag("SYSTEMD_NSS_RESOLVE_CACHE", 0, SD_RESOLVED_NO_CACHE) |
+                query_flag("SYSTEMD_NSS_RESOLVE_ZONE", 0, SD_RESOLVED_NO_ZONE) |
+                query_flag("SYSTEMD_NSS_RESOLVE_TRUST_ANCHOR", 0, SD_RESOLVED_NO_TRUST_ANCHOR) |
+                query_flag("SYSTEMD_NSS_RESOLVE_NETWORK", 0, SD_RESOLVED_NO_NETWORK);
+}
+
+enum nss_status _nss_resolve_gethostbyname4_r(
+                const char *name,
+                struct gaih_addrtuple **pat,
+                char *buffer, size_t buflen,
+                int *errnop, int *h_errnop,
+                int32_t *ttlp) {
+
+        _cleanup_(varlink_unrefp) Varlink *link = NULL;
+        _cleanup_(json_variant_unrefp) JsonVariant *cparams = NULL;
+        _cleanup_(resolve_hostname_reply_destroy) ResolveHostnameReply p = {};
+        JsonVariant *rparams, *entry;
+        int r;
+
+        PROTECT_ERRNO;
+        NSS_ENTRYPOINT_BEGIN;
+
+        assert(name);
+        assert(pat);
+        assert(buffer);
+        assert(errnop);
+        assert(h_errnop);
+
+        r = connect_to_resolved(&link);
+        if (r < 0)
+                goto fail;
+
+        r = json_build(&cparams, JSON_BUILD_OBJECT(
+                                       JSON_BUILD_PAIR("name", JSON_BUILD_STRING(name)),
+                                       JSON_BUILD_PAIR("flags", JSON_BUILD_UNSIGNED(query_flags()))));
+        if (r < 0)
+                goto fail;
+
+        /* Return NSS_STATUS_UNAVAIL when communication with systemd-resolved fails, allowing falling
+         * back to other nss modules. Treat all other error conditions as NOTFOUND. This includes
+         * DNSSEC errors and suchlike. (We don't use UNAVAIL in this case so that the nsswitch.conf
+         * configuration can distinguish such executed but negative replies from complete failure to
+         * talk to resolved). */
+        const char *error_id;
+        r = varlink_call(link, "io.systemd.Resolve.ResolveHostname", cparams, &rparams, &error_id, NULL);
+        if (r < 0)
+                goto fail;
+        if (!isempty(error_id)) {
+                if (error_shall_try_again(error_id))
+                        goto try_again;
+                if (error_shall_fallback(error_id))
+                        goto fail;
+                if (streq(error_id, "io.systemd.Resolve.NoSuchResourceRecord"))
+                        goto no_data;
+                goto not_found;
+        }
+
+        r = json_dispatch(rparams, resolve_hostname_reply_dispatch_table, json_dispatch_flags, &p);
+        if (r < 0)
+                goto fail;
+        if (json_variant_is_blank_object(p.addresses))
+                goto not_found;
+
+        size_t n_addresses = 0;
+        JSON_VARIANT_ARRAY_FOREACH(entry, p.addresses) {
+                AddressParameters q = {};
+
+                r = json_dispatch(entry, address_parameters_dispatch_table, json_dispatch_flags, &q);
+                if (r < 0)
+                        goto fail;
+
+                if (!IN_SET(q.family, AF_INET, AF_INET6))
+                        continue;
+
+                if (q.address_size != FAMILY_ADDRESS_SIZE(q.family)) {
+                        r = -EINVAL;
+                        goto fail;
+                }
+
+                n_addresses++;
+        }
+
+        const char *canonical = p.name ?: name;
+        size_t l = strlen(canonical);
+        size_t idx, ms = ALIGN(l+1) + ALIGN(sizeof(struct gaih_addrtuple)) * n_addresses;
+
+        if (buflen < ms) {
+                UNPROTECT_ERRNO;
+                *errnop = ERANGE;
+                *h_errnop = NETDB_INTERNAL;
+                return NSS_STATUS_TRYAGAIN;
+        }
+
+        /* First, append name */
+        char *r_name = buffer;
+        memcpy(r_name, canonical, l + 1);
+        idx = ALIGN(l + 1);
+
+        /* Second, append addresses */
+        struct gaih_addrtuple *r_tuple = NULL,
+                *r_tuple_first = (struct gaih_addrtuple*) (buffer + idx);
+
+        JSON_VARIANT_ARRAY_FOREACH(entry, p.addresses) {
+                AddressParameters q = {};
+
+                r = json_dispatch(entry, address_parameters_dispatch_table, json_dispatch_flags, &q);
+                if (r < 0)
+                        goto fail;
+
+                if (!IN_SET(q.family, AF_INET, AF_INET6))
+                        continue;
+
+                r_tuple = (struct gaih_addrtuple*) (buffer + idx);
+                r_tuple->next = (struct gaih_addrtuple*) ((char*) r_tuple + ALIGN(sizeof(struct gaih_addrtuple)));
+                r_tuple->name = r_name;
+                r_tuple->family = q.family;
+                r_tuple->scopeid = ifindex_to_scopeid(q.family, &q.address, q.ifindex);
+                memcpy(r_tuple->addr, &q.address, q.address_size);
+
+                idx += ALIGN(sizeof(struct gaih_addrtuple));
+        }
+
+        assert(r_tuple);  /* We had at least one address, so r_tuple must be set */
+        r_tuple->next = NULL;  /* Override last next pointer */
+
+        assert(idx == ms);
+
+        if (*pat)
+                **pat = *r_tuple_first;
+        else
+                *pat = r_tuple_first;
+
+        if (ttlp)
+                *ttlp = 0;
+
+        /* Explicitly reset both *h_errnop and h_errno to work around
+         * https://bugzilla.redhat.com/show_bug.cgi?id=1125975 */
+        *h_errnop = NETDB_SUCCESS;
+        h_errno = 0;
+
+        return NSS_STATUS_SUCCESS;
+
+fail:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        *h_errnop = NO_RECOVERY;
+        return NSS_STATUS_UNAVAIL;
+
+not_found:
+        *h_errnop = HOST_NOT_FOUND;
+        return NSS_STATUS_NOTFOUND;
+
+no_data:
+        *h_errnop = NO_DATA;
+        return NSS_STATUS_NOTFOUND;
+
+try_again:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        *h_errnop = TRY_AGAIN;
+        return NSS_STATUS_TRYAGAIN;
+}
+
+enum nss_status _nss_resolve_gethostbyname3_r(
+                const char *name,
+                int af,
+                struct hostent *result,
+                char *buffer, size_t buflen,
+                int *errnop, int *h_errnop,
+                int32_t *ttlp,
+                char **canonp) {
+
+        _cleanup_(varlink_unrefp) Varlink *link = NULL;
+        _cleanup_(json_variant_unrefp) JsonVariant *cparams = NULL;
+        _cleanup_(resolve_hostname_reply_destroy) ResolveHostnameReply p = {};
+        JsonVariant *rparams, *entry;
+        int r;
+
+        PROTECT_ERRNO;
+        NSS_ENTRYPOINT_BEGIN;
+
+        assert(name);
+        assert(result);
+        assert(buffer);
+        assert(errnop);
+        assert(h_errnop);
+
+        if (af == AF_UNSPEC)
+                af = AF_INET;
+
+        if (!IN_SET(af, AF_INET, AF_INET6)) {
+                r = -EAFNOSUPPORT;
+                goto fail;
+        }
+
+        r = connect_to_resolved(&link);
+        if (r < 0)
+                goto fail;
+
+        r = json_build(&cparams, JSON_BUILD_OBJECT(JSON_BUILD_PAIR("name", JSON_BUILD_STRING(name)),
+                                                   JSON_BUILD_PAIR("family", JSON_BUILD_INTEGER(af)),
+                                                   JSON_BUILD_PAIR("flags", JSON_BUILD_UNSIGNED(query_flags()))));
+        if (r < 0)
+                goto fail;
+
+        const char *error_id;
+        r = varlink_call(link, "io.systemd.Resolve.ResolveHostname", cparams, &rparams, &error_id, NULL);
+        if (r < 0)
+                goto fail;
+        if (!isempty(error_id)) {
+                if (error_shall_try_again(error_id))
+                        goto try_again;
+                if (error_shall_fallback(error_id))
+                        goto fail;
+                if (streq(error_id, "io.systemd.Resolve.NoSuchResourceRecord"))
+                        goto no_data;
+                goto not_found;
+        }
+
+        r = json_dispatch(rparams, resolve_hostname_reply_dispatch_table, json_dispatch_flags, &p);
+        if (r < 0)
+                goto fail;
+        if (json_variant_is_blank_object(p.addresses))
+                goto not_found;
+
+        size_t n_addresses = 0;
+        JSON_VARIANT_ARRAY_FOREACH(entry, p.addresses) {
+                AddressParameters q = {};
+
+                r = json_dispatch(entry, address_parameters_dispatch_table, json_dispatch_flags, &q);
+                if (r < 0)
+                        goto fail;
+
+                if (!IN_SET(q.family, AF_INET, AF_INET6))
+                        continue;
+
+                if (q.address_size != FAMILY_ADDRESS_SIZE(q.family)) {
+                        r = -EINVAL;
+                        goto fail;
+                }
+
+                n_addresses++;
+        }
+
+        const char *canonical = p.name ?: name;
+
+        size_t alen = FAMILY_ADDRESS_SIZE(af);
+        size_t l = strlen(canonical);
+
+        size_t idx, ms = ALIGN(l + 1) + n_addresses * ALIGN(alen) + (n_addresses + 2) * sizeof(char*);
+
+        if (buflen < ms) {
+                UNPROTECT_ERRNO;
+                *errnop = ERANGE;
+                *h_errnop = NETDB_INTERNAL;
+                return NSS_STATUS_TRYAGAIN;
+        }
+
+        /* First, append name */
+        char *r_name = buffer;
+        memcpy(r_name, canonical, l+1);
+        idx = ALIGN(l+1);
+
+        /* Second, create empty aliases array */
+        char *r_aliases = buffer + idx;
+        ((char**) r_aliases)[0] = NULL;
+        idx += sizeof(char*);
+
+        /* Third, append addresses */
+        char *r_addr = buffer + idx;
+
+        size_t i = 0;
+        JSON_VARIANT_ARRAY_FOREACH(entry, p.addresses) {
+                AddressParameters q = {};
+
+                r = json_dispatch(entry, address_parameters_dispatch_table, json_dispatch_flags, &q);
+                if (r < 0)
+                        goto fail;
+
+                if (q.family != af)
+                        continue;
+
+                if (q.address_size != alen) {
+                        r = -EINVAL;
+                        goto fail;
+                }
+
+                memcpy(r_addr + i*ALIGN(alen), &q.address, alen);
+                i++;
+        }
+
+        assert(i == n_addresses);
+        idx += n_addresses * ALIGN(alen);
+
+        /* Fourth, append address pointer array */
+        char *r_addr_list = buffer + idx;
+        for (i = 0; i < n_addresses; i++)
+                ((char**) r_addr_list)[i] = r_addr + i*ALIGN(alen);
+
+        ((char**) r_addr_list)[i] = NULL;
+        idx += (n_addresses + 1) * sizeof(char*);
+
+        assert(idx == ms);
+
+        result->h_name = r_name;
+        result->h_aliases = (char**) r_aliases;
+        result->h_addrtype = af;
+        result->h_length = alen;
+        result->h_addr_list = (char**) r_addr_list;
+
+        if (ttlp)
+                *ttlp = 0;
+
+        if (canonp)
+                *canonp = r_name;
+
+        /* Explicitly reset both *h_errnop and h_errno to work around
+         * https://bugzilla.redhat.com/show_bug.cgi?id=1125975 */
+        *h_errnop = NETDB_SUCCESS;
+        h_errno = 0;
+
+        return NSS_STATUS_SUCCESS;
+
+fail:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        *h_errnop = NO_RECOVERY;
+        return NSS_STATUS_UNAVAIL;
+
+not_found:
+        *h_errnop = HOST_NOT_FOUND;
+        return NSS_STATUS_NOTFOUND;
+
+no_data:
+        *h_errnop = NO_DATA;
+        return NSS_STATUS_NOTFOUND;
+
+try_again:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        *h_errnop = TRY_AGAIN;
+        return NSS_STATUS_TRYAGAIN;
+}
+
+typedef struct ResolveAddressReply {
+        JsonVariant *names;
+        uint64_t flags;
+} ResolveAddressReply;
+
+static void resolve_address_reply_destroy(ResolveAddressReply *p) {
+        assert(p);
+
+        json_variant_unref(p->names);
+}
+
+static const JsonDispatch resolve_address_reply_dispatch_table[] = {
+        { "names", JSON_VARIANT_ARRAY,         json_dispatch_variant, offsetof(ResolveAddressReply, names), JSON_MANDATORY },
+        { "flags", _JSON_VARIANT_TYPE_INVALID, json_dispatch_uint64,  offsetof(ResolveAddressReply, flags), 0              },
+        {}
+};
+
+typedef struct NameParameters {
+        int ifindex;
+        char *name;
+} NameParameters;
+
+static void name_parameters_destroy(NameParameters *p) {
+        assert(p);
+
+        free(p->name);
+}
+
+static const JsonDispatch name_parameters_dispatch_table[] = {
+        { "ifindex", JSON_VARIANT_INTEGER, json_dispatch_ifindex, offsetof(NameParameters, ifindex), 0              },
+        { "name",    JSON_VARIANT_STRING,  json_dispatch_string,  offsetof(NameParameters, name),    JSON_MANDATORY },
+        {}
+};
+
+enum nss_status _nss_resolve_gethostbyaddr2_r(
+                const void* addr, socklen_t len,
+                int af,
+                struct hostent *result,
+                char *buffer, size_t buflen,
+                int *errnop, int *h_errnop,
+                int32_t *ttlp) {
+
+        _cleanup_(varlink_unrefp) Varlink *link = NULL;
+        _cleanup_(json_variant_unrefp) JsonVariant *cparams = NULL;
+        _cleanup_(resolve_address_reply_destroy) ResolveAddressReply p = {};
+        JsonVariant *rparams, *entry;
+        int r;
+
+        PROTECT_ERRNO;
+        NSS_ENTRYPOINT_BEGIN;
+
+        assert(addr);
+        assert(result);
+        assert(buffer);
+        assert(errnop);
+        assert(h_errnop);
+
+        if (!IN_SET(af, AF_INET, AF_INET6)) {
+                UNPROTECT_ERRNO;
+                *errnop = EAFNOSUPPORT;
+                *h_errnop = NO_DATA;
+                return NSS_STATUS_UNAVAIL;
+        }
+
+        if (len != FAMILY_ADDRESS_SIZE(af)) {
+                r = -EINVAL;
+                goto fail;
+        }
+
+        r = connect_to_resolved(&link);
+        if (r < 0)
+                goto fail;
+
+        r = json_build(&cparams, JSON_BUILD_OBJECT(JSON_BUILD_PAIR("address", JSON_BUILD_BYTE_ARRAY(addr, len)),
+                                                   JSON_BUILD_PAIR("family", JSON_BUILD_INTEGER(af)),
+                                                   JSON_BUILD_PAIR("flags", JSON_BUILD_UNSIGNED(query_flags()))));
+        if (r < 0)
+                goto fail;
+
+        const char* error_id;
+        r = varlink_call(link, "io.systemd.Resolve.ResolveAddress", cparams, &rparams, &error_id, NULL);
+        if (r < 0)
+                goto fail;
+        if (!isempty(error_id)) {
+                if (error_shall_try_again(error_id))
+                        goto try_again;
+                if (error_shall_fallback(error_id))
+                        goto fail;
+                goto not_found;
+        }
+
+        r = json_dispatch(rparams, resolve_address_reply_dispatch_table, json_dispatch_flags, &p);
+        if (r < 0)
+                goto fail;
+        if (json_variant_is_blank_object(p.names))
+                goto not_found;
+
+        size_t ms = 0, idx;
+
+        JSON_VARIANT_ARRAY_FOREACH(entry, p.names) {
+                _cleanup_(name_parameters_destroy) NameParameters q = {};
+
+                r = json_dispatch(entry, name_parameters_dispatch_table, json_dispatch_flags, &q);
+                if (r < 0)
+                        goto fail;
+
+                ms += ALIGN(strlen(q.name) + 1);
+        }
+
+        size_t n_names = json_variant_elements(p.names);
+        ms += ALIGN(len) +                    /* the address */
+              2 * sizeof(char*) +             /* pointer to the address, plus trailing NULL */
+              n_names * sizeof(char*);        /* pointers to aliases, plus trailing NULL */
+
+        if (buflen < ms) {
+                UNPROTECT_ERRNO;
+                *errnop = ERANGE;
+                *h_errnop = NETDB_INTERNAL;
+                return NSS_STATUS_TRYAGAIN;
+        }
+
+        /* First, place address */
+        char *r_addr = buffer;
+        memcpy(r_addr, addr, len);
+        idx = ALIGN(len);
+
+        /* Second, place address list */
+        char *r_addr_list = buffer + idx;
+        ((char**) r_addr_list)[0] = r_addr;
+        ((char**) r_addr_list)[1] = NULL;
+        idx += sizeof(char*) * 2;
+
+        /* Third, reserve space for the aliases array, plus trailing NULL */
+        char *r_aliases = buffer + idx;
+        idx += sizeof(char*) * n_names;
+
+        /* Fourth, place aliases */
+        char *r_name = buffer + idx;
+
+        size_t i = 0;
+        JSON_VARIANT_ARRAY_FOREACH(entry, p.names) {
+                _cleanup_(name_parameters_destroy) NameParameters q = {};
+
+                r = json_dispatch(entry, name_parameters_dispatch_table, json_dispatch_flags, &q);
+                if (r < 0)
+                        goto fail;
+
+                size_t l = strlen(q.name);
+                char *z = buffer + idx;
+                memcpy(z, q.name, l + 1);
+
+                if (i > 0)
+                        ((char**) r_aliases)[i - 1] = z;
+                i++;
+
+                idx += ALIGN(l + 1);
+        }
+        ((char**) r_aliases)[n_names - 1] = NULL;
+
+        assert(idx == ms);
+
+        result->h_name = r_name;
+        result->h_aliases = (char**) r_aliases;
+        result->h_addrtype = af;
+        result->h_length = len;
+        result->h_addr_list = (char**) r_addr_list;
+
+        if (ttlp)
+                *ttlp = 0;
+
+        /* Explicitly reset both *h_errnop and h_errno to work around
+         * https://bugzilla.redhat.com/show_bug.cgi?id=1125975 */
+        *h_errnop = NETDB_SUCCESS;
+        h_errno = 0;
+
+        return NSS_STATUS_SUCCESS;
+
+fail:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        *h_errnop = NO_RECOVERY;
+        return NSS_STATUS_UNAVAIL;
+
+not_found:
+        *h_errnop = HOST_NOT_FOUND;
+        return NSS_STATUS_NOTFOUND;
+
+try_again:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        *h_errnop = TRY_AGAIN;
+        return NSS_STATUS_TRYAGAIN;
+}
+
+NSS_GETHOSTBYNAME_FALLBACKS(resolve);
+NSS_GETHOSTBYADDR_FALLBACKS(resolve);
diff --git a/src/nss-resolve/nss-resolve.sym b/src/nss-resolve/nss-resolve.sym
new file mode 100644
index 0000000..ecc958e
--- /dev/null
+++ b/src/nss-resolve/nss-resolve.sym
@@ -0,0 +1,19 @@
+/***
+  SPDX-License-Identifier: LGPL-2.1-or-later
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+***/
+
+{
+global:
+        _nss_resolve_gethostbyname_r;
+        _nss_resolve_gethostbyname2_r;
+        _nss_resolve_gethostbyname3_r;
+        _nss_resolve_gethostbyname4_r;
+        _nss_resolve_gethostbyaddr_r;
+        _nss_resolve_gethostbyaddr2_r;
+local: *;
+};